Chronic hepatitis C virus (HCV) infection is now the leading cause of hepatocellular carcinoma (HCC), a highly lethal cancer with rapidly increasing incidence in the U.S. How HCV causes liver cancer is not well understood because of the lack of a small animal model for HCV pathogenesis. The overarching goal of this interdisciplinary, multi-PI project is to refine a recently developed humanized mouse model of hepatitis C (the AFC8-hu mouse) that possesses both a chimeric human liver and a functioning human immune system, and to use this model to elucidate viral mechanisms of carcinogenesis responsible for HCV-associated HCC. AFC8-hu mice engrafted with CD34+ human hematopoietic stem cells and EpCAM+ human hepatoblasts and hepatic stem cells achieve ~18% hepatic chimerism, are permissive for HCV infection, and develop a human HCV- specific T cell response with hepatic inflammation when infected with HCV. Remarkably, HCV infection of these mice results in significant hepatic fibrosis and evidence of oxidative DNA damage - hallmarks of chronic hepatitis C in human patients. Three interrelated specific aims are proposed to refine this model and to apply it to the study of the mechanisms of carcinogenesis responsible for HCV-associated HCC. Aim 1 focuses on optimizing protocols to enhance hepatic chimerism in AFC8-hu mice, and to infect AFC8-hu mice with genotype 1a HCVcc produced in cell culture from recombinant DNA, thereby providing a system supporting reverse molecular viral genetics studies of HCV-mediated carcinogenesis. In Aim 2, p53 will be inactivated in human hepatoblasts prior to transplantation into AFC8 mice to provide for accelerated development of human liver cancer in HCV-infected mice, and to facilitate discovery of novel determinants of HCV-mediated hepatocarcinogenesis. Aim 3 will utilize a reverse molecular genetics strategy to test the hypothesis that the disruption of critical tumor suppressor function by HCV promotes cancer in the genotoxic environment of immune-mediated hepatic inflammation and oxidative stress, and to specifically assess the role played by the targeted destruction of the retinoblastoma protein by HCV and sequestration of the tumor suppressor DDX3 by HCV core protein. Further development of the AFC8-hu mouse model, coupled with the use of infectious genotype 1a H77S virus produced from recombinant cDNA, will provide a robust and completely unique experimental system in which the complex interplay of direct and indirect mechanisms of carcinogenesis can be elucidated. The results of these studies will add significantly to current understanding of how HCV infection leads to the development of HCC, and advance the development and evaluation of new preventative and therapeutic strategies to lessen the considerable burden of morbidity and mortality imposed by liver cancer in patients with chronic hepatitis C.